Voltage converting device, computer readable recording medium with program recorded thereon for causing computer to execute failure processing, and failure processing method

ABSTRACT

A control device detects whether or not an up-converter fails, based on a DC voltage from a voltage sensor, an output voltage from a voltage sensor, and a duty ratio in controlling switching of NPN transistors. If a failure in the up-converter is detected, the control device then controls an inverter and an AC motor such that regenerative electric power generation in the AC motor is prohibited.

TECHNICAL FIELD

The present invention relates to a voltage converting device capable ofprocessing a failure in a voltage converter converting a DC voltage froma DC power supply to an output voltage, a computer readable recordingmedium with a program recorded thereon for causing a computer to executefailure processing, and a failure processing method.

BACKGROUND ART

Recently, hybrid vehicles and electric vehicles have attracted greatattention as environment-friendly vehicles. Some hybrid vehicles are nowcommercially available.

The hybrid vehicle includes, as a power source, a DC power supply, aninverter and a motor driven by the inverter, in addition to theconventional engine. Specifically, the engine is driven to generatepower while DC voltage from the DC power supply is converted into ACvoltage by the inverter to rotate the motor by the AC voltage andaccordingly generate power. The electric vehicle includes, as a powersource, a DC power supply, an inverter and a motor driven by theinverter.

Some hybrid or electric vehicles are designed to boost DC voltage fromthe DC power supply by an up-converter and to supply the boosted DCvoltage to the inverter driving the motor.

Japanese Patent Laying-Open No. 2-308935 discloses an electric device300 shown in FIG. 13. This electric device 300 is mounted on a hybridvehicle. Referring to FIG. 13, electric device 300 includes a DC powersupply 310, a bypass line 311, a relay 312, a boost chopper 320, acapacitor 326, an inverter 330, an electric device body 350, and a fieldmagnet controller 360.

Bypass line 311 and relay 312 are connected in series between a powersupply line and the positive electrode of DC power supply 310.

Boost chopper 320 includes a reactor 321, MOS transistors 322, 323, anddiodes 324, 325. Reactor 321 has one end connected to the power supplyline of DC power supply 310 and the other end connected to theintermediate point between MOS transistor 322 and MOS transistor 323.MOS transistors 322 and 323 are connected in series between the powersupply line and a ground line. MOS transistor 322 has its drainconnected to the power supply line. MOS transistor 323 has its sourceconnected to the ground line. Diodes 324, 325 are each connected betweenthe source and drain of the corresponding one of MOS transistors 322,323 for allowing current to flow from the source side to the drain side.

Inverter 330 is constituted of a U-phase arm 343, a V-phase arm 344 anda W-phase arm 345. U-phase arm 343, V-phase arm 344 and W-phase arm 345are connected in parallel between the power supply line and the groundline.

U-phase arm 343 is formed of MOS transistors 331 and 332 connected inseries. V-phase arm 344 is formed of MOS transistors 333 and 334connected in series. W-phase arm 345 is formed of MOS transistors 335and 336 connected in series. Diodes 337-342 are each connected betweenthe source and drain of the corresponding one of MOS transistors 331-336for allowing current to flow from the source side to the drain side.

Electric device body 350 includes three phase coils and serves as apower generator and a motor for an engine. The U, V, W phase arms ofinverter 330 have their respective intermediate points connected to therespective ends of the U, V, W phase coils of electric device body 350.The other end of the U-phase coil is connected to the intermediate pointbetween MOS transistors 331 and 332. The other end of the V-phase coilis connected to the intermediate point between MOS transistors 333 and334. The other end of the W-phase coil is connected to the intermediatepoint between MOS transistors 335 and 336.

Field magnet controller 360 includes a diode 361, an NPN transistor 362and a base amplifier 363. Diode 361 is connected between the positiveterminal F+ of the field coil of electric device body 350 and thecollector of NPN transistor 362. NPN transistor 362 is connected betweenthe negative terminal F− of the field coil and the ground line forreceiving at its base a voltage from base amplifier 363. Base amplifier363 is responsive to a control signal from a control device (not shown)to output a prescribed voltage to the base of NPN transistor 362 forturning on/off NPN transistor 362.

DC power supply 310 outputs a DC voltage. When relay 312 is turned on bythe control signal from the control device (not shown), bypass line 311supplies the voltage on both ends of capacitor 326 to DC power supply310. Boost chopper 320 has its MOS transistors 322, 323 turned on/off bythe control device (not shown) and boosts the DC voltage supplied fromDC power supply 310 to provide an output voltage to inverter 330. Boostchopper 320 also down-converts the DC voltage generated by electricdevice body 350 and converted by inverter 330 to charge DC power supply310, at the time of regenerative braking of the hybrid vehicle includingelectric device 300.

Capacitor 326 smoothes the DC voltage supplied from boost chopper 320and supplies the smoothed DC voltage to inverter 330.

Inverter 330 receives the DC voltage from capacitor 326 to convert theDC voltage to an AC voltage based on the control from the control device(not shown) and drives electric device body 350 as a driving motor.Field magnet controller 360 allows current to flow in the field coil inaccordance with the time period during which NPN transistor 362 isturned on. Electric device body 350 is therefore driven as a drivingmotor to generate torque specified by a torque command value. Inregenerative braking of the hybrid vehicle including electric device300, inverter 330 also converts an AC voltage generated by electricdevice body 350 to a DC voltage based on the control from the controldevice and supplies the converted DC voltage to boost chopper 320through capacitor 326.

In electric device 300, a failure in boost chopper 320 is detected bydetecting that the output voltage of boost chopper 320 becomes lowerthan a reference value. When the failure in boost chopper 320 isdetected, relay 312 is turned on by the control signal from the controldevice, and bypass line 311 directly supplies the voltage on both endsof capacitor 326 to DC power supply 310.

In electric device 300 disclosed in Japanese Patent Laying-Open No.2-308935, however, when boost chopper 320 fails, the voltage on bothends of capacitor 326 is supplied to DC power supply 310 without beingdown-converted. Therefore, if a large amount of power is generated byelectric device body 350, a high voltage will be applied to both ends ofcapacitor 326, resulting in that the withstand voltage performance ofcapacitor 326 must be improved, thereby increasing costs.

DISCLOSURE OF THE INVENTION

An object of the present invention is therefore to provide a voltageconverting device capable of processing a failure in an up-converterwithout improving withstand voltage performance of a capacitor placed atan input of an inverter.

Another object of the present invention is to provide a failureprocessing method capable of processing a failure in an up-converterwithout improving withstand voltage performance of a capacitor placed atan input of an inverter.

A further object of the present invention is to provide a computerreadable recording medium with a program recorded thereon for causing acomputer to execute failure processing for an up-converter, withoutimproving withstand voltage performance of a capacitor placed at aninput of an inverter.

A voltage converting device in accordance with the present inventionincludes an electric load, a capacitor, a down-converter, and controlmeans. The electric load has an electric power generating function. Thecapacitor is connected to an input of the electric load. Thedown-converter down-converts a voltage of the capacitor. The controlmeans controls the electric load such that electric power generation inthe electric load is prohibited or an amount of electric power generatedby the electric load is decreased, when the down-converter fails.

Preferably, the down-converter has a voltage-up-converting function.

Preferably, the electric load is a motor having an electric powergenerating function. The control means restricts a regenerative electricpower generating function of the motor, when the down-converter fails.

Preferably, the control means prohibits regenerative electric powergeneration of the motor.

Preferably, the voltage converting device further includes anotherelectric load. Another electric load is different from the motor. Thecontrol means restricts an amount of regenerative electric powergenerated by the motor to a value smaller than power consumption inanother electric load.

A voltage converting device in accordance with the present inventionincludes first and second electric loads, a capacitor, a down-converter,and control means. The first electric load has an electric powergenerating function. The capacitor is connected to an input of the firstelectric load. The down-converter down-converts a voltage of thecapacitor. The second electric load is different from the first electricload. The control means controls the second electric load such that anamount of power consumption in the second electric load is increased,when the down-converter fails.

Preferably, the second electric load is a motor. The control meanscontrols the motor such that it outputs positive torque.

In accordance with the present invention, a computer readable recordingmedium with a program recorded thereon for causing a computer to executefailure processing in a voltage converting device is provided. Thevoltage converting device includes an electric load having an electricpower generating function, a capacitor connected to an input of theelectric load, and a down-converter down-converting a voltage of thecapacitor. The program causes the computer to execute a first step ofdetecting a failure in the down-converter, and a second step ofcontrolling the electric load such that electric power generation in theelectric load is prohibited or an amount of electric power generated bythe electric load is decreased, when the failure in the down-converteris detected at the first step.

Preferably, the electric load is a motor having an electric powergenerating function. In the second step of the program, a regenerativeelectric power generating function of the motor is restricted.

Preferably, in the second step of the program, regenerative electricpower generation of the motor is prohibited.

Preferably, the voltage converting device further includes anotherelectric load different from the electric load. In the second step ofthe program, an amount of regenerative electric power generated by themotor is restricted to a value smaller than power consumption in anotherelectric load.

In accordance with the present invention, a computer readable recordingmedium with a program recorded thereon for causing a computer to executefailure processing in a voltage converting device is provided. Thevoltage converting device includes a first electric load having anelectric power generating function, a capacitor connected to an input ofthe electric load, a second electric load different from the firstelectric load, and a down-converter down-converting a voltage of thecapacitor. The program causes the computer to execute a first step ofdetecting a failure in the down-converter and a second step ofincreasing an amount of power consumption in the second electric load,when the failure in the down-converter is detected at the first step.

Preferably, the second electric load is a motor. In the second step ofthe program, the motor is controlled such that it outputs positivetorque, when the failure in the down-converter is detected at the firststep.

In accordance with the present invention, a failure processing method ina voltage converting device including an electric load having anelectric power generating function, a capacitor connected to an input ofthe electric load, and a down-converter down-converting a voltage of thecapacitor includes: a first step of detecting a failure in thedown-converter; and a second step of controlling the electric load suchthat electric power generation in the electric load is prohibited or anamount of electric power generated by the electric load is decreased,when the failure in the down-converter is detected at the first step.

Preferably, the electric load is a motor having an electric powergenerating function. In the second step, a regenerative electric powergenerating function of the motor is restricted.

Preferably, in the second step, regenerative electric power generationof the motor is prohibited.

Preferably, the voltage converting device further includes anotherelectric load different from the electric load. In the second step ofthe failure processing method, an amount of regenerative electric powergenerated by the motor is restricted to a value smaller than powerconsumption in another electric load.

In accordance with the present invention, a failure processing method ina voltage converting device including a first electric load having anelectric power generating function, a capacitor connected to an input ofthe electric load, a second electric load different from the firstelectric load, and a down-converter down-converting a voltage of thecapacitor includes: a first step of detecting a failure in thedown-converter; and a second step of increasing an amount of powerconsumption in the second electric load, when the failure in thedown-converter is detected at the first step.

Preferably, the second electric load is a motor. In the second step ofthe failure processing method, the motor is controlled such that itoutputs positive torque, when the failure in the down-converter isdetected at the first step.

In the present invention, when an up-converter fails, electric powergeneration in an electric load connected to an output of theup-converter is prohibited or a power generation amount in the electricload is restricted. Furthermore, when the up-converter fails, a powergeneration amount in one of two electric loads is controlled to be equalto or less than energy consumption in the other electric load.

Therefore, in accordance with the present invention, even if theup-converter fails, it is possible to prevent a voltage equal to orhigher than a withstand voltage from being applied to a capacitorconnected to an input of an electric load (including first and secondelectric loads).

The foregoing and other objects, features, aspects and advantages of thepresent invention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram of a voltage converting device inaccordance with a first embodiment.

FIG. 2 is a functional block diagram of a control device shown in FIG.1.

FIG. 3 is a functional block diagram illustrating a function of motortorque control means shown in FIG. 2.

FIG. 4 is a flowchart illustrating an operation of processing a failurein an up-converter in the first embodiment.

FIG. 5 is a schematic block diagram of a voltage converting device inaccordance with a second embodiment.

FIG. 6 is a functional block diagram of a control device shown in FIG.5.

FIG. 7 is a functional block diagram illustrating a function of motortorque control means shown in FIG. 6.

FIG. 8 is a flowchart illustrating an operation of processing a failurein an up-converter in the second embodiment.

FIG. 9 is a schematic block diagram of a voltage converting device inaccordance with a third embodiment.

FIG. 10 is a functional block diagram of a control device shown in FIG.9.

FIG. 11 is a functional block diagram illustrating a function of motortorque control means shown in FIG. 10.

FIG. 12 is a flowchart illustrating an operation of processing a failurein an up-converter in the third embodiment.

FIG. 13 is a schematic block diagram of a conventional electric device.

BEST MODES FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described in detail withreference to the drawings. It is noted that in the figures the same orcorresponding parts will be denoted with the same reference charactersand description thereof will not be repeated.

[First Embodiment]

Referring to FIG. 1, a voltage converting device 100 in accordance witha first embodiment of the present invention includes a DC power supplyB, voltage sensors 10, 13, system relays SR1, SR2, capacitors C1, C2, anup-converter 12, an inverter 14, a current sensor 24, a control device30, and an AC motor M1. AC motor M1 is a drive motor for generatingtorque for driving a driving wheel of a hybrid or electric vehicle.Alternatively, the motor may serve as a power generator driven by theengine and as an electric motor for the engine. For example, it may beincorporated in a hybrid vehicle to start the engine.

Up-converter 12 includes a reactor L1, NPN transistors Q1, Q2, anddiodes D1, D2. Reactor L1 has one end connected to a power supply lineof DC power supply B and the other end connected to the intermediatepoint between NPN transistors Q1 and Q2, that is, between the emitter ofNPN transistor Q1 and the collector of NPN transistor Q2. NPNtransistors Q1 and Q2 are connected in series between the power supplyline and a ground line. The collector of NPN transistor Q1 is connectedto the power supply line, and the emitter of NPN transistor Q2 isconnected to the ground line. Diodes D1, D2 are each arranged betweenthe collector and emitter of the corresponding one of NPN transistorsQ1, Q2 for allowing current to flow the emitter side to the collectorside.

Inverter 14 is constituted of a U-phase arm 15, a V-phase arm 16 and aW-phase arm 17. U-phase arm 15, V-phase arm 16 and W-phase arm 17 areconnected in parallel between the power supply line and the ground line.

U-phase arm 15 is formed of NPN transistors Q3 and Q4 connected inseries. V-phase arm 16 is formed of NPN transistors Q5 and Q6 connectedin series. W-phase arm 17 is formed of NPN transistors Q7 and Q8connected in series. Diodes D3-D8 are each connected between thecollector and emitter of the corresponding one of NPN transistors Q3-Q8for allowing current to flow from the emitter side to the collectorside.

The U, V, W phase arms have their respective intermediate pointsconnected to the respective ends of the U, V, W phase coils of AC motorM1. Specifically, AC motor M1 is a three-phase permanent magnet motorwith respective three coils of U, V and W phases each having one endconnected commonly to the center. The other end of the U-phase coil isconnected to the intermediate point between NPN transistors Q3 and Q4,the other end of the V-phase coil is connected to the intermediate pointbetween NPN transistors Q5 and Q6, and the other end of the W-phase coilis connected to the intermediate point between NPN transistors Q7 andQ8.

DC power supply B is formed of a nickel-hydrogen or lithium-ionsecondary battery. Voltage sensor 10 detects a DC voltage Vb from DCpower supply B to output the detected DC voltage Vb to control device30. System relays SR1, SR2 are turned on/off by a signal SE from controldevice 30. More specifically, system relays SR1, SR2 are turned on bysignal SE of H (logical high) level from control device 30 and turnedoff by signal SE of L (logical low) level from control device 30.

Capacitor C1 smoothes DC voltage Vb supplied from DC power supply B toprovide the smoothed DC voltage to up-converter 12.

Up-converter 12 boosts the DC voltage from capacitor C1 to supply theboosted voltage to inverter 14. More specifically, up-converter 12receives a signal PWMU from control device 30 to boost the DC voltageand supply the boosted DC voltage to inverter 14 in accordance with aperiod in which NPN transistor Q2 is turned on by signal PWMU. In thiscase, NPN transistor Q1 is kept off by signal PWMU. Further,up-converter 12 receives a signal PWMD from control device 30 todown-convert the DC voltage supplied from inverter 14 via capacitor C2and accordingly charge DC power supply B.

Capacitor C2 smoothes the DC voltage from up-converter 12 to supply thesmoothed DC voltage to inverter 14. Voltage sensor 13 detects thevoltage on both ends of capacitor C2, i.e., an output voltage Vm ofup-converter 12 (which corresponds to an input voltage to inverter 14)and outputs the detected output voltage Vm to control device 30.

Inverter 14 receives the DC voltage from capacitor C2 to convert, basedon a signal PWMI1 from control device 30, the DC voltage into an ACvoltage and accordingly drive AC motor M1 to generate positive torque.Inverter 14 also converts, based on a signal PWMI2 from control device30, the DC voltage to an AC voltage and drives AC motor M1 to outputzero torque. Then, AC motor M1 is driven to generate zero or positivetorque as designated by a torque command value TR.

In regenerative braking of a hybrid or electric vehicle includingvoltage converting device 100, inverter 14 converts an AC voltagegenerated by AC motor M1 into a DC voltage according to a signal PWMI3from control device 30 and supplies the converted DC voltage toup-converter 12 via capacitor C2. Here, “regenerative braking” includesbraking which is caused when a driver of a hybrid or electric vehiclemanages the foot brake and which is accompanied by regenerative powergeneration as well as deceleration (or stopping of acceleration) of thevehicle by releasing the accelerator (pedal) in driving without managingthe foot brake, which is also accompanied by regenerative powergeneration.

Current sensor 24 detects a motor current MCRT flowing to AC motor M1 tooutput the detected motor current MCRT to control device 30.

Control device 30 generates, based on torque command value TR and motorrotation number MRN supplied from an externally placed ECU (electricalcontrol unit), DC voltage Vb from voltage sensor 10, output voltage Vmfrom voltage sensor 13, and motor current MCRT from current sensor 24,signal PWMU for driving up-converter 12 and signals PWMI1 and PVMI2 fordriving inverter 14, following a method as described hereinbelow, andprovides the generated signals PWMU and PWMI1, 2 to up-converter 12 andinverter 14 respectively.

Signal PWMU is a signal for driving up-converter 12 when up-converter 12converts the DC voltage from capacitor C1 to output voltage Vm. Whenup-converter 12 converts the DC voltage to output voltage Vm, controldevice 30 controls the feedback of output voltage Vm and generatessignal PWMU for driving up-converter 12 so that output voltage Vmbecomes a voltage command Vdc_com as instructed. A method of generatingsignal PWMU will be described later.

Control device 30 receives from the external ECU a signal RGE indicatingthat the hybrid or electric vehicle enters a regenerative braking mode,to generate signal PWMI3 for converting the AC voltage generated by ACmotor M1 into a DC voltage and output the signal to inverter 14. In thiscase, switching of NPN transistors Q3-Q8 of inverter 14 is controlled bysignal PWMI3. In this way, inverter 14 converts the AC voltage generatedby motor M1 into the DC voltage to supply the DC voltage to up-converter12.

Furthermore, control device 30 receives from the external ECU signal RGEindicating that the hybrid or electric vehicle enters the regenerativebraking mode, to generate signal PWMD for down-converting the DC voltagefrom inverter 14 and output the generated signal PWMD to up-converter12. In this way, the AC voltage generated by AC motor M1 is convertedinto DC voltage, which is down-converted to be supplied to DC powersupply B.

Moreover, control device 30 determines whether or not up-converter 12fails, based on a duty ratio in controlling the switching of NPNtransistors Q1, Q2, DC voltage Vb from voltage sensor 10 and voltage Vmfrom voltage sensor 13. When it is determined that up-converter 12fails, control device 30 receives signal RGE from external ECU tocontrol inverter 14 such that regenerative electric power generation inAC motor M1 is prohibited. More specifically, when up-converter 12fails, control device 30 generates and outputs to inverter 14 signalPWMI1 for driving AC motor Ml to output positive torque or signal PWMI2for driving AC motor M1 to output zero torque in the regenerativebraking mode.

Moreover, control device 30 generates signal SE for turning on/offsystem relays SR1, SR2 and supplies signal SE to system relays SR1, SR2.

FIG. 2 is a functional block diagram of control device 30. Referring toFIG. 2, control device 30 includes motor torque control means 301 andvoltage conversion control means 302. Motor torque control means 301generates, based on torque command value TR, output voltage Vb of DCpower supply B, motor current MCRT, motor rotation number MRN, andoutput voltage Vm of up-converter 12, signal PWMU for turning on/off NPNtransistors Q1, Q2 of up-converter 12 and signal PVMI1 for turningon/off NPN transistors Q3-Q8 of inverter 14, following a methoddescribed hereinafter, and outputs the generated signals PWMU and PWMI1to up-converter 12 and inverter 14, respectively, when AC motor M1 isdriven to output positive torque.

Motor torque control means 301 determines whether or not up-converter 12fails based on a duty ratio in controlling the switching of NPNtransistors Q1, Q2 and voltages Vb, Vm. When it is determined thatup-converter 12 fails, motor torque control means 301 generates a signalEMG in response to signal RGE from external ECU to output signal EMG tovoltage conversion control means 302, and also generates signal PWMI1for driving AC motor M1 to output positive torque or signal PWMI2 fordriving the AC motor to output zero torque, to output signal PVMI1 orPWMI2 to inverter 14.

In regenerative braking, voltage conversion control means 302 receivesfrom external ECU signal RGE indicating that the hybrid or electricvehicle enters the regenerative braking mode, to generate signal PVWMI3for converting the AC voltage generated by AC motor M1 to a DC voltageand output signal PWMI3 to inverter 14.

In regenerative braking, voltage conversion control means 302 alsoreceives signal RGE from external ECU to generate signal PWMD fordown-converting the DC voltage supplied from inverter 14 and outputsignal PWMD to up-converter 12. In this way, up-converter 12 serves as abidirectional converter as it can also down-convert the voltage bysignal PWMD for down-converting a DC voltage.

Furthermore, voltage conversion control means 302 receives signal EMGfrom motor torque control means 301 to stop generation of signals PWMI3and PWMD.

FIG. 3 is a functional block diagram of motor torque control means 301.Referring to FIG. 3, motor torque control means 301 includes a phasevoltage calculating unit 40 for controlling the motor, a PWM signalconverting unit 42 for the inverter, an inverter input voltage commandcalculating unit 50, a duty ratio calculating unit 52 for the converter,a PWM signal converting unit 54 for the converter, and a determinationunit 56.

Phase voltage calculating unit 40 receives from voltage sensor 13 outputvoltage Vm of up-converter 12, that is, the input voltage to inverter14, receives from current sensor 24 motor current MCRT flowing to eachphase of AC motor M1, receives torque command value TR from the externalECU, and receives signals DTE 1, 2 from determination unit 56. Whenreceiving signal DTE1 from determination unit 56, phase voltagecalculating unit 40 calculates, based on torque command value TR, outputvoltage Vm and motor current MCRT, a voltage to be applied to the coilof each phase of AC motor M1 and supplies the calculated voltage to PWMsignal converting unit 42.

Phase voltage calculating unit 40 receives signal DTE2 fromdetermination unit 56 to calculate a voltage to be applied to the coilof each phase of AC motor M1 for allowing AC motor M1 to output zero orpositive torque, and then supply the calculated voltage to PWM signalconverting unit 42.

PWM signal converting unit 42 generates, based on the calculated voltagesupplied from phase voltage calculating unit 40, signals PWMI1, PWMI2for actually turning on/off each of NPN transistors Q3-Q8 of inverter 14and supplies the generated signals PWMI1, PWMI2 to each of NPNtransistors Q3-Q8 of inverter 14.

Switching of NPN transistors Q3-Q8 each is thus controlled and NPNtransistors Q3-Q8 accordingly control the current to be supplied to eachphase of AC motor M1 so that AC motor M1 generates zero or positivetorque. In this way, the motor drive current is controlled so that themotor torque is output according to torque command value TR.

On the other hand, inverter input voltage command calculating unit 50calculates an optimum value (target value) of an inverter input voltage,that is, voltage command Vdc_com, based on torque command value TR andmotor rotation number MRN, and provides the calculated voltage commandVdc_com to duty ratio calculating unit 52.

Duty ratio calculating unit 52 calculates, based on DC voltage Vb outputfrom voltage sensor 10 (also referred to as “battery voltage Vb”), aduty ratio for setting voltage Vm from voltage sensor 13 at the optimumvalue supplied from inverter input voltage command calculating unit 50.Duty ratio calculating unit 52 outputs the calculated duty ratio to PWMsignal converting unit 54 and determination unit 56.

PWM signal converting unit 54 generates, based on the duty ratiosupplied from duty ratio calculating unit 52, signal PWMU for turningon/off NPN transistors Q1, Q2 of up-converter 12 and provides thegenerated signal PWMU to up-converter 12.

A greater amount of electric power is accumulated by reactor L1 byincreasing on-duty of NPN transistor Q2 which is the lower transistor ofup-converter 12, and accordingly a higher-voltage output is obtained.The voltage on the power supply line is decreased by increasing theon-duty of the upper transistor, i.e., NPN transistor Q1. The duty ratioof NPN transistors Q1 and Q2 can thus be controlled to control thevoltage on the power supply line such that the voltage on the powersupply line is an arbitrary voltage of at least the output voltage of DCpower supply B.

Determination unit 56 receives battery voltage Vb from voltage sensor10, voltage Vm from voltage sensor 13, duty ratio DR from duty ratiocalculating unit 52, and signal RGE from external ECU. Determinationunit 56 multiplies battery voltage Vb by duty ratio DR and determineswhether or not a product AP resulting from the multiplication matchesvoltage Vm from voltage sensor 13. If the product AP matches voltage Vm,determination unit 56 determines that up-converter 12 operates normally,and generates and outputs signal DTE1 to phase voltage calculating unit40. If product AP does not match voltage Vm, determination unit 56determines that up-converter 12 fails, and receives signal RGE fromexternal ECU to generate and output signals EMG and DTE2 to voltageconversion control means 302 and phase voltage calculating unit 40,respectively.

FIG. 4 is a flowchart illustrating an operation of processing a failurein up-converter 12 in the first embodiment. Referring to FIG. 4, uponthe start of a series of operations, determination unit 56 detects afailure in up-converter 12, following the aforementioned method, basedon battery voltage Vb from voltage sensor 10, voltage Vm from voltagesensor 13 and duty ratio DR from duty ratio calculating unit 52 (stepS10). When detecting a failure in up-converter 12 and receiving signalRGE from external ECU, determination unit 56 generates and outputssignals EMG and DTE2 to voltage conversion control means 302 and motortorque control means 301, respectively.

In response, voltage conversion control means 302 stops generation ofsignals PWMI3 and PWMD. In response to signal DTE2 from determinationunit 56, phase voltage calculating unit 40 calculates a voltage to beapplied to the coil of each phase in generating signal PWMI1 for drivingAC motor M1 to output positive torque or signal PVMI2 for driving ACmotor M1 to output zero torque, and outputs the calculated voltage toPWM signal converting unit 42.

PWM signal converting unit 42 generates signal PWMI1 or PWMI2 based onthe calculated voltage from phase voltage calculating unit 40 to outputPWMI1 or PWMI2 to inverter 14. Inverter 14 drives AC motor M1 to outputzero or positive torque in response to signal PVVMI1 or PWMI2 from PWMsignal converting unit 42, and regenerative electric power generation isprohibited (step S20). A series of operations then ends.

Therefore, even if control device 30 receives from external ECU signalRGE indicating regenerative power generation, in the event of a failurein up-converter 12, regenerative electric power generation in AC motorM1 is prohibited, thereby preventing DC voltage equal to or higher thanthe withstand voltage from being applied to capacitor C2.

Inverter 14 may be stopped to prohibit regenerative electric powergeneration in AC motor M1 in the event of a failure in up-converter 12.In the present embodiment, however, regenerative electric powergeneration is prohibited with AC motor M1 being kept driven so as tooutput the instructed torque immediately when external ECU torquesupplies command value TR for outputting positive torque.

Returning to FIG. 1, the operation in voltage converting device 100 willbe described. Control device 30 receives torque command value TR fromexternal ECU to generate and output signal SE at H level to systemrelays SR1, SR2 for turning on system relays SR1, SR2. Control device 30also generates signals PWMU and PWMI1 for controlling up-converter 12and inverter 14 such that AC motor M1 generates torque command value TRand output signals PWMU and PWMI1 to up-converter 12 and inverter 14,respectively.

DC power supply B outputs DC voltage Vb, and system relays SR1, SR2supply DC voltage Vb to capacitor C1. Capacitor C1 smoothes the receivedDC voltage Vb and supplies the smoothed DC voltage to up-converter 12.

Then, NPN transistors Q1, Q2 of up-converter 12 are turned on/off inresponse to signal PWMU from control device 30 and convert DC voltage Vbto output voltage Vm to be supplied to inverter 14. Voltage sensor 13detects output voltage Vm that is a voltage on both ends of capacitor C2and outputs the detected output voltage Vm to control device 30.Capacitor C2 smoothes output voltage Vm of up-converter 12 and suppliesthe smoothed output voltage Vm to inverter 14.

NPN transistors Q3-Q8 of inverter 14 are turned on/off in response tosignal PWMI1 from control device 30. Inverter 14 converts the DC voltageto an AC voltage and allows prescribed AC current to flow to each of U,V and W phases of AC motor M1 so that AC motor M1 generates torque asdesignated by torque command value TR. In this way, AC motor M1generates torque as designated by torque command value TR.

When the hybrid or electric vehicle including voltage converting device100 enters the regenerative braking mode, control device 30 receivesfrom external ECU signal RGE indicating the regenerative braking mode,to generate and output signals PWMI3 and PWMD to inverter 14 andup-converter 12, respectively.

AC motor M1 generates an AC voltage and supplies the generated ACvoltage to inverter 14. Inverter 14 then converts the AC voltage to a DCvoltage in accordance with signal PVWMI3 from control device 30 andsupplies the converted DC voltage to up-converter 12 via capacitor C2.

Up-converter 12 down-converts the DC voltage in accordance with signalPWMD from control device 30 and supplies the down-converted DC voltageto DC power supply B to charge DC power supply B.

Then, control device 30 determines, following the aforementioned method,whether or not up-converter 12 fails, based on DC voltage Vb, voltage Vmand duty ratio DR for controlling the switching of NPN transistors Q1,Q2. If up-converter 12 fails, control device 30 controls inverter 14such that regenerative electric power generation in AC motor M1 in theregenerative braking mode is prohibited.

In this manner, in voltage converting device 100, regenerative electricpower generation in AC motor M1 in the regenerative braking mode isprohibited when up-converter 12 fails. This can prevent application of avoltage equal to or higher than the withstand voltage to capacitor C2.

The failure processing method in accordance with the present inventionincludes detecting a failure in up-converter 12 and prohibitingregenerative electric power generation according to the flowchart shownin FIG. 4.

The failure processing in motor torque control means 301 is actuallycontrolled by a CPU (Central Processing Unit). CPU reads a programincluding the steps of the flowchart shown in FIG. 4 from an ROM (ReadOnly Memory) and executes the read program to control the failureprocessing for up-converter 12 according to the flowchart shown in FIG.4. Thus, ROM corresponds to a computer (CPU) readable recording mediumwith a program recorded thereon with the steps of the flowchart in FIG.4.

It is noted that AC motor M1 forms an “electric load”.

Here, “prohibiting regenerative (electric power generation)” meansdriving AC motor M1 to output zero or positive torque.

In accordance with the first embodiment, the voltage converting deviceincludes a control device that controls an inverter such thatregenerative electric power generation in an AC motor is prohibited whenan up-converter fails, thereby preventing application of a voltage equalto or higher than a withstand voltage to a capacitor provided at theinput of the inverter.

[Second Embodiment]

Referring to FIG. 5, a voltage converting device 100A in accordance witha second embodiment is the same as voltage converting device 100 exceptthat control device 30 in voltage converting device 100 is replaced witha control device 30A and that a rectifier 18, a generator G1 and acurrent sensor 25 are added.

Inverter 14 and rectifier 18 are connected in parallel between nodes N1and N2 on both ends of capacitor C2. Generator G1 is connected to anengine 55.

Rectifier 18 is constituted of a U-phase arm 19, a V-phase arm 20 and aW-phase arm 21. U-phase arm 19, V-phase arm 20 and W-phase arm 21 areconnected in parallel between the power supply line and the ground line.U-phase arm 19 is formed of diodes D9 and D1 connected in series.V-phase arm 20 is formed of diodes D11 and D12 connected in series.W-phase arm 21 is formed of diodes D13 and D14 connected in series. Theintermediate point between diode D9 and diode D10 is connected to theend of U-phase coil of generator G1. The intermediate point betweendiodes D11 and diode D12 is connected to the end of the V-phase coil ofgenerator G1. The intermediate point between diode D13 and diode D14 isconnected to the end of the W-phase coil of generator G1.

Rectifier 18 rectifies the AC voltage generated by generator G1 andsupplies the rectified DC voltage to up-converter 12 via capacitor C2.Generator G1 generates an AC voltage by rotation of a rotor, which iscaused by rotating power of engine 55, and supplies the generated ACvoltage to rectifier 18.

Current sensor 25 detects a generator current GCRT flowing to each phaseof generator G1 and outputs the detected generator current GCRT tocontrol device 30A.

Control device 30A generates signals PWMI1 and PWMI3, among signalsPWMI1-3 for driving inverter 14, and outputs signals PVMI1 and PWMI3 toinverter 14. The method of generating signals PWMI1 and PWMI3 is thesame as described in the first embodiment.

When control device 30A determines that up-converter 12 fails, followingthe aforementioned method, it calculates an energy consumption Pm in ACmotor M1 based on an accelerator opening degree ACC and motor rotationnumber MRN from external ECU and calculates a power generation amount(the amount of generated electric power) Pg in generator G1 based onvoltage Vm from voltage sensor 13 and generator current GCRT fromcurrent sensor 25. Control device 30A then generates and outputs signalRDN to an engine ECU 65 for setting the rotation number of engine 55such that power generation amount Pg in generator G1 is equal to or lessthan energy consumption Pm in AC motor M1.

Control device 30A has the same function as control device 30 in theother respects.

Engine 55 is controlled by engine ECU 65 for outputting prescribedtorque for driving a drive wheel as well as for transmitting a rotatingpower to generator G1. Engine ECU 65 controls engine 55. Engine ECU 65receives signal RDN from control device 30A to hold or decrease therotation number of engine 55.

Referring to FIG. 6, control device 30A is the same as control device 30except that motor torque control means 301 of control device 30 isreplaced with motor torque control means 301A.

Motor torque control means 301A generates and outputs signals PWMU andPWMI1 to up-converter 12 and inverter 14, respectively, following thesame method as in motor torque control means 301.

Furthermore, motor torque control means 30 1A determines whether or notup-converter 12 fails, following the same method as in motor torquecontrol means 301. When motor torque control means 301A determines thatup-converter 12 fails, it calculates energy consumption Pm in AC motorM1 based on accelerator opening degree ACC and motor rotation number MRNand calculates power generation amount Pg in generator G1 based ongenerator current GCRT and voltage Vm. Furthermore, motor torque controlmeans 301A generates and outputs signal RDN to engine ECU 65 for settingthe rotation number of engine 55 such that power generation amount Pg isequal to or less than energy consumption Pm.

Referring to FIG. 7, motor torque control means 301A is the same asmotor torque control means 301 except that determination unit 56 ofmotor torque control means 301 is replaced with a determination unit 56Aand that a calculating unit 58 and a control unit 60 are added.

Determination unit 56A determines whether or not up-converter 12 fails,following the same method as in determination unit 56. If it isdetermined that up-converter 12 is normal, determination unit 56Agenerates and outputs signal DTE1 to control unit 60. On the other hand,if it is determined that up-converter 12 fails, determination unit 56Agenerates and outputs signal DTE2 to control unit 60.

Calculating unit 58 calculates energy consumption Pm of AC motor Mlbased on accelerator opening degree ACC and motor rotation number MRNfrom external ECU. Calculating unit 58 also calculates power generationamount Pg in generator G1 based on voltage Vm from voltage sensor 13 andgenerator current GCRT from current sensor 25. Calculating unit 58 thenoutputs the calculated energy consumption Pm and power generation amountPg to control unit 60.

When control unit 60 receives signal DTE1 from determination unit 56A,it does not generate a control signal. When control unit 60 receivessignal DTE2 from determination unit 56A, it generates and outputs signalRDN to engine ECU 65 for setting the rotation number of engine 55 suchthat power generation amount Pg is equal to or less than energyconsumption Pm.

FIG. 8 is a flowchart illustrating the operation of processing a failurein up-converter 12 in the second embodiment. Referring to FIG. 8, uponthe start of a series of operations, determination unit 56A of controldevice 30A detects a failure in up-converter 12, based on batteryvoltage Vb from voltage sensor 10, voltage Vm from voltage sensor 13 andduty ratio DR from duty ratio calculating unit 52, and generates andoutputs signal DTE2 to control unit 60 (step S10). Calculating unit 58then receives accelerator opening degree ACC from external ECU (stepS11) and receives a vehicle speed, i.e., motor rotation number MRN fromexternal ECU (step S12).

Calculating unit 58 then calculates torque T from accelerator openingdegree ACC based on that torque T output by AC motor M1 is proportionalto accelerator opening degree ACC. Calculating unit 58 then calculatesenergy consumption Pm in AC motor M1 based on the calculated torque Tand motor rotation number MRN from external ECU (step S13).

Calculating unit 58 also calculates power generation amount Pg ingenerator G1 based on voltage Vm from voltage sensor 13 and generatorcurrent GCRT from current sensor 25 (step S14). Calculating unit 58 thenoutputs the calculated energy consumption Pm and power generation amountPg to control unit 60.

In response to signal DTE2 from determination unit 56A, control unit 60generates and outputs to engine ECU 65 signal RDN for setting therotation number of engine 55 such that power generation amount Pg isequal to or less than energy consumption Pm. In other words, controlunit 60 controls generator G1 by setting an upper limit of powergeneration amount Pg in generator G1 such that power generation amountPg does not exceed energy consumption Pm in AC motor M1.

More specifically, control unit 60 receives signal DTE2 fromdetermination unit 56A to compare power generation amount Pg fromcalculating unit 58 with energy consumption Pm. When power generationamount Pg is equal to or less than energy consumption Pm, control unit60 generates a signal RDN1 for holding the present rotation number ofengine 55 and outputs signal RDN1 to engine ECU 65. When powergeneration amount Pg is greater than energy consumption Pm, control unit60 generates a signal RDN2 for decreasing the present rotation number ofengine 55 and outputs signal RDN2 to engine ECU 65. Signal RDN thereforeincludes signals RDN1 and RDN2.

Engine ECU 65 holds the rotation number in response to signal RDN1 fromcontrol unit 60 or controls engine 55 to decrease the rotation number inresponse to signal RDN2 from control unit 60. The rotation number ofengine 55 is held at a certain value or decreased. Power generationamount Pg in generator G1 is thus decreased to energy consumption Pm orless (step S15).

The electric power generated by generator G1 is all consumed in AC motorM1, thereby preventing application of a voltage equal to or higher thana withstand voltage to both ends of capacitor C2.

Returning to FIG. 5, the operation in voltage converting device 100Awill be described. The operations are as described in the firstembodiment in that control device 30A generates signals PWMU and PWMI1for driving up-converter 12 and inverter 14 to output the same toup-converter 12 and inverter 14, respectively, up-converter 12up-converts DC voltage Vb to output voltage Vm, and inverter 14 drivesAC motor M1.

Generator G1 generates electric power using the rotating power of engine55 and supplies the generated AC voltage to rectifier 18. Rectifier 18rectifies the AC voltage to supply DC voltage to capacitor C2. Currentsensor 25 detects generator current GCRT and outputs the detectedcurrent to control device 30A.

Control device 30A determines whether or not up-converter 12 fails,following the aforementioned method. If up-converter 12 fails, controldevice 30A calculates energy consumption Pm of AC motor M1 and powergeneration amount Pg of generator G1. Then, control device 30A generatessignal RDN for setting the rotation number of engine 55 such that powergeneration amount Pg is equal to or less than energy consumption Pm, andcontrol device 30A outputs signal RDN to engine ECU 65. In response tosignal RDN from control device 30A, engine ECU 65 holds or decreases therotation number to rotate engine 55. Power generation amount Pg ofgenerator G1 is thus controlled to be equal to or less than energyconsumption Pm of AC motor M1.

When AC motor M1 enters the regenerative braking mode, control device30A receives signal RGE from external ECU and generates and outputssignals PWMI3 and PWMD to inverter 14 and up-converter 12, respectively.

AC motor M1 generates an AC voltage and supplies the generated ACvoltage to inverter 14. Inverter 14 then converts the AC voltage to a DCvoltage in accordance with signal PWMI3 from control device 30A tosupply the converted DC voltage to up-converter 12 via capacitor C2.

Up-converter 12 down-converts the DC voltage in accordance with signalPWMD from control device 30A to supply the down-converted DC voltage toDC power supply B to charge DC power supply B.

As described above, in -voltage converting device 100A, if up-converter12 fails, power generation amount Pg in generator G1 is controlled to beequal to or less than energy consumption Pm in AC motor M1. Therefore, avoltage equal to or higher than a withstand voltage is prevented frombeing applied to capacitor C2.

The failure processing method in accordance with the present inventionincludes detecting a failure in up-converter 12 according to theflowchart shown in FIG. 8 and controlling power generation amount Pg ingenerator G1 to be equal to or less than energy consumption Pm in ACmotor M1.

The failure processing in motor torque control means 301A is actuallycontrolled by CPU. CPU reads a program including the steps in theflowchart shown in FIG. 8 from an ROM and executes the read program tocontrol the failure processing for up-converter 12 according to theflowchart shown in FIG. 8. Therefore, ROM corresponds to a computer(CPU) readable recording medium with a program recorded thereon with thesteps in the flowchart shown in FIG. 8.

The other details are the same as in the first embodiment.

In accordance with the second embodiment, the voltage converting deviceincludes a control device that controls a power generation amount of agenerator to be equal to or less than an energy consumption of an ACmotor, in the event of a failure in an up-converter, thereby preventingapplication of a voltage equal to or higher than a withstand voltage toa capacitor provided at an input of an inverter.

[Third Embodiment]

Referring to FIG. 9, a voltage converting device 100B in accordance witha third embodiment is the same as voltage converting device 100A exceptthat control device 30A, rectifier 18, generator G1, and current sensor25 of voltage converting device 100A are replaced with a control device30B, an inverter 31, an AC motor M2, and a current sensor 28,respectively.

It is noted that, in voltage converting device 100B, current sensor 24detects and outputs motor current MCRT1 to control device 30B. AC motorM2 is connected to engine 55. Capacitor C2 receives the DC voltage fromup-converter 12 via nodes N1, N2, smoothes the received DC voltage, andsupplies the smoothed DC voltage to inverter 14 as well as to inverter31. Inverter 14 converts, based on a signal PWMI11 from control device30B, the DC voltage from capacitor C2 to an AC voltage for driving ACmotor M1, and converts, based on a signal PMW13, the AC voltagegenerated by AC motor M1 into a DC voltage.

Inverter 31 has the same configuration as inverter 14. Inverter 31converts, based on a signal PWMI21 from control device 30B, the DCvoltage from capacitor C2 into an AC voltage for driving AC motor M2,and converts, based on a signal PWMI23, the AC voltage generated by ACmotor M2 into a DC voltage. Current sensor 28 detects motor currentMCRT2 flowing to each phase of AC motor M2 and outputs the detectedmotor current MCRT2 to control device 30B.

Control device 30B receives DC voltage Vb output by DC power supply Bfrom voltage sensor 10, receives motor currents MCRT1, MCRT2 fromcurrent sensors 24, 28, respectively, receives output voltage Vm ofup-converter 12 (that is, the input voltage to inverters 14, 31) fromvoltage sensor 13, and receives torque command values TR1, TR2, motorrotation numbers MRN1, MRN2 and accelerator opening degree ACC fromexternal ECU. Control device 30B generates, based on DC voltage Vb,output voltage Vm, motor current MCRT1, torque command value TR1, andmotor rotation number MRN1, signal PWMI11 for controlling the switchingof NPN transistors Q3-Q8 of inverter 14, following the aforementionedmethod, when inverter 14 drives AC motor M1. Control device 30B thenoutputs the generated signal PWMI11 to inverter 14.

Control device 30B also generates, based on DC voltage Vb, outputvoltage Vm, motor current MCRT2, torque command value TR2, and motorrotation number MRN2, signal PWMI21 for controlling the switching of NPNtransistors Q3-Q8 of inverter 31, following the aforementioned method,when inverter 31 drives AC motor M2. Control device 30B then outputs thegenerated signal PWMI21 to inverter 31.

Control device 30B further generates, based on DC voltage Vb, outputvoltage Vm, motor current MCRT1 (or MCRT2), torque command value TR1 (orTR2), and motor rotation number MRN1 (or MRN2), signal PWMU forcontrolling the switching of NPN transistors Q1, Q2 of up-converter 12,following the aforementioned method, when inverter 14 or 31 drives ACmotor M1 or M2. Control device 30B then outputs the generated signalPWMU to up-converter 12.

Control device 30B also generates, in the regenerative braking mode, asignal PWM13 for converting the AC voltage generated by AC motor M1 intoa DC voltage, or a signal PWM23 for converting the AC voltage generatedby AC motor M2 into a DC voltage, and outputs the generated signal PWM13or PWM23 to inverter 14 or inverter 31, respectively. In this case,control device 30B generates and outputs signal PWMD to up-converter 12for controlling up-converter 12 such that up-converter 12 down-convertsthe DC voltage from inverter 14 or 31 to charge DC power supply B.

Furthermore, control device 30B determines whether or not up-converter12 fails, following the aforementioned method. When up-converter 12fails, control device 30B calculates energy Pm in AC motor M1 based onaccelerator opening degree ACC and motor rotation number MRN1. Controldevice 30B then determines whether AC motor M1 is in a powering mode ora regenerative mode based on the calculated energy Pm. If AC motor M1 isin the powering mode, control device 30B regards the calculated energyPm as an energy consumption Pm1. When AC motor M1 is in the poweringmode, AC motor M2 is in the regenerative mode. Accordingly, controldevice 30B calculates a power generation amount Pg2 of AC motor M2 andcontrols power generation amount Pg2 of AC motor M2 to be equal to orless than energy consumption Pm1 of AC motor M1, following the method asdescribed in the second embodiment.

When AC motor M1 is in the regenerative mode, control device 30B regardsthe calculated energy Pm as a power generation amount Pg1 and thengenerates and outputs a signal CUT to engine ECU 65 so that the fuel ofengine 55 is cut off. In addition, control device 30B controls AC motorM2 such that it outputs positive torque. Control device 30B thencalculates an energy consumption Pm2 of AC motor M2, and if a sumPg1+Pm2 of power generation amount Pg1 and energy consumption Pm2 isnegative, control device 30B controls AC motor M1 such that powergeneration amount Pg1 in AC motor M1 is equal to or less than energyconsumption Pm2.

In addition, control device 30B generates and outputs signal SE tosystem relays SR1, SR2 for turning on/off system relays SR1, SR2.

Referring to FIG. 10, control device 30B includes motor torque controlmeans 301B and voltage conversion control means 302A. Motor torquecontrol means 301B generates signal PVMI11 based on motor current MCRT1,torque command value TR1, motor rotation number MRN1, DC voltage Vb, andvoltage Vm, and outputs the generated signal PWVMI11 to inverter 14.Motor torque control means 301B generates signal PWMI21 based on motorcurrent MCRT2, torque command value TR2, motor rotation number MRN2, DCvoltage Vb, and voltage Vm, and outputs the generated signal PWMI21 toinverter 31.

Motor torque control means 301B also generates signal PWMU based on DCvoltage Vb, voltage Vm, motor current MCRT1 (or MCRT2), torque commandvalue TR1 (or TR2), and motor rotation number MRN1 (or MRN2), andoutputs the generated signal PWMU to up-converter 12.

Furthermore, motor torque control means 301B determines whetherup-converter 12 fails, following the aforementioned method. If it isdetermined that up-converter 12 fails, motor torque control means 301Bcalculates energy Pm in AG motor M1 based on accelerator opening degreeACC and motor rotation number MRN1, and further determines whether ACmotor M1 is in the powering mode or in the regenerative mode based onthe calculated energy Pm. More specifically, motor torque control device301B determines that AC motor M1 is in the powering mode when thecalculated energy Pm is positive, and determines that AC motor M1 is inthe regenerative mode when energy Pm is negative.

When AC motor M1 is in the powering mode, motor torque control means301B calculates power generation amount Pg2 in AC motor M2 based onvoltage Vm from voltage sensor 13 and motor current MCRT2 from currentsensor 28. Motor torque control means 301B then generates signal RDN forsetting the rotation number of engine 55 such that power generationamount Pg2 in AC motor M2 is equal to or less than energy consumptionPm1 and outputs the generated signal RDN to engine ECU 65. Motor torquecontrol means 301B also generates signal RGE2 and outputs the generatedsignal RGE2 to voltage conversion control means 302A.

On the other hand, when AC motor M1 is in the regenerative mode, motortorque control means 301B generates and outputs signal CUT for cuttingoff the fuel for engine 55 to engine ECU 65, signal RGE1 to voltageconversion control means 302A, and signal PWMI21 for causing AC motor M2to output positive torque to inverter 31. Motor torque control means301B calculates energy consumption Pm2 in AC motor M2. If the sum ofpower generation amount Pg1 in AC motor M1 and energy consumption Pm2 inAC motor M2 is negative, motor torque control means 301B controls ACmotor M1 such that power generation amount Pg1 in AC motor M1 is equalto or less than energy consumption Pm2 in AC motor M2. Motor torquecontrol means 301B holds the present state of AC motors M1, M2, if thesum of power generation amount Pg1 and energy consumption Pm2 ispositive.

Voltage conversion control means 302A receives from external ECU signalRGE indicating that the hybrid or electric vehicle including voltageconverting device 100B enters the regenerative braking mode, to generatesignals PWM13, 23 and signal PWMD, output the generated signals PWM 13,23 to inverters 14, 31, respectively, and output signal PWMD toup-converter 12.

Voltage conversion control means 302A also receives signal RGE1 frommotor torque control means 301B to generate and output signal PWMI13 toinverter 14 for controlling power generation amount Pg1 in AC motor M1to be equal to or less than energy consumption Pm2 in AC motor M2.

Voltage conversion control means 302A also receives signal RGE2 frommotor torque control means 301B to generate and output signal PWMI23 toinverter 31 for controlling power generation amount Pg2 in AC motor M2to be equal to or less than energy consumption Pm1 in AC motor M1.

Referring to FIG. 11, motor torque control means 301B is the same asmotor torque control means 301A except that phase voltage calculatingunit 40 for controlling the motor, determination unit 56A, calculatingunit 58, and control unit 60 of motor torque control means 301A arereplaced with a phase voltage calculating unit 40A for controlling themotor, a determination unit 56B, a calculating unit 58A, and a controlunit 60A, respectively.

Phase voltage calculating unit 40A calculates a voltage to be applied toeach phase of AC motor M1 based on output voltage Vm of up-converter 12,motor current MCRT1 and torque command value TR1, and calculates avoltage to be applied to each phase of AC motor M2 based on outputvoltage Vm, motor current MCRT2 and torque command value TR2. Phasevoltage calculating unit 40A then outputs the voltage calculated for ACmotor M1 or M2 to PWM signal converting unit 42.

Phase voltage calculating unit 40A receives torque command value TREfrom control unit 60A to calculate a voltage to be applied to each phaseof AC motor M2, based on torque command value TRE, output voltage Vm andmotor current MCRT2, and then outputs the calculated voltage to PWMconverting unit 42.

PWM signal converting unit 42 receives a voltage for AC motor M1 fromphase voltage calculating unit 40A to generate and output signal PWMI11to inverter 14 based on the received voltage. PWM signal converting unit42 receives a voltage for AC motor M2 from phase voltage calculatingunit 40A to generate and output signal PWMI21 to inverter 31 based onthe received voltage.

Inverter input voltage command calculating unit 50 calculates voltagecommand Vdc_com based on torque command value TR1 and motor rotationnumber MRN1 (or torque command value TR2 and motor rotation numberMRN2), and outputs the calculated voltage command Vdc_com to duty ratiocalculating unit 52.

Determination unit 56B determines whether or not up-converter 12 fails,based on battery voltage Vb from voltage sensor 10, output voltage Vmfrom voltage sensor 13 and duty ratio DR from duty ratio calculatingunit 52, following the aforementioned method. If it is determined thatup-converter 12 fails, determination unit 56B then determines whetherenergy Pm from calculating unit 58A is positive or negative. If energyPm is positive, determination unit 56B determines that AC motor M1 is inthe powering mode, and regards energy Pm as energy consumption Pm1. Onthe other hand, if energy Pm is negative, determination unit 56Bdetermines that AC motor M1 is in the regenerative mode, and regardsenergy Pm as power generation amount Pg1.

When AC motor M1 is in the powering mode, determination unit 56Bgenerates and outputs a signal DTE3 to control unit 60A for indicating adetermination result that power generation amount Pg2 in AC motor M2should be controlled to be equal to or less than energy consumption Pm1in AC motor M1.

When AC motor M1 is in the regenerative mode, determination unit 56Bgenerates and outputs a signal DTE4 to control unit 60A for indicating adetermination result that the fuel for engine 55 should be cut off.

After outputting signal DTE4 to control unit 60A, determination unit 56Breceives from calculating unit 58A the sum Pg1+Pm2 of power generationamount Pg1 in AC motor M1 and energy consumption Pm2 in AC motor M2, anddetermines whether the received sum Pg1+Pm2 is positive or negative. Ifthe sum Pg1+Pm2 is negative, determination unit 56B generates andoutputs a signal DTE5 to control unit 60A for indicating a determinationresult that power generation amount Pg1 in AC motor M1 should becontrolled to be equal to or less than energy consumption Pm2 in ACmotor M2.

If the sum Pg1+Pm2 is positive, determination unit 56B generates andoutputs a signal DTE6 to control unit 60A for indicating a determinationresult that the present state in AC motors M1, M2 should be held.

Calculating unit 58A calculates torque T output by AC motor M1 based onaccelerator opening degree ACC from external ECU, calculates energy Pmin AC motor M1 based on the calculated torque T and motor rotationnumber MRN1 from external ECU, and outputs the calculated energy Pm todetermination unit 56B and control unit 60A.

Calculating unit 58A calculates power generation amount Pg2 in AC motorM2 based on output voltage Vm from voltage sensor 13 and motor currentMCRT2 from current sensor 28 and outputs the calculated power generationamount Pg2 to control unit 60A.

Furthermore, calculating unit 58A receives torque command value TRE fromcontrol unit 60A to calculate energy consumption Pm2 in AC motor M2based on torque command value TRE and motor rotation number MRN2 fromexternal ECU, and outputs the calculated energy consumption Pm2 tocontrol unit 60A. Calculating unit 58A then calculates the sum of energyPm in AC motor M1 and energy consumption Pm2 as the sum of powergeneration amount Pg1 in AC motor M1 and energy consumption Pm2, andoutputs the calculated sum Pg1+Pm2 to determination unit 56B.

In response to signal DTE3 from determination unit 56B, control unit 60Aregards energy Pm from calculating unit 58A as energy consumption Pm1 inAC motor M1 and compares power generation amount Pg2 from calculatingunit 58A with energy consumption Pm1. Control unit 60A then generatesand outputs signal RDN (including RDN1 and RDN2) to engine ECU65 forsetting the rotation number of engine 55 such that power generationamount Pg2 is equal to or less than energy consumption Pm1. Morespecifically, if power generation amount Pg2 is equal to or less thanenergy consumption Pm1, control unit 60A generates and outputs signalRDN1 to engine ECU 65 for holding the present rotation number of engine55. If power generation amount Pg2 is greater than energy consumptionPm1, control unit 60A generates and outputs signal RDN2 to engine ECU 65for decreasing the present rotation number of engine 55 so that powergeneration amount Pg2 is equal to or less than energy consumption Pm1.Control unit 60A also generates and outputs signal RGE2 to voltageconversion control means 302A.

In response to signal DTE4 from determination unit 56B, control unit 60Agenerates signal CUT and torque command value TRE and outputs signal CUTto engine ECU-65 and torque command value TRE to phase voltagecalculating unit 40A. Torque command value TRE is a command value fordesignating positive torque to be output by AC motor M2 so that therotation number of engine 55 is maintained or increased.

In response to signal DTE5 from determination unit 56B, control unit 60Aregards energy Pm from calculating unit 58A as power generation amountPg1 in AC motor M1 and compares power generation amount Pg1 with energyconsumption Pm2 from calculating unit 58A. Control unit 60A thengenerates and outputs signal RGE1 to voltage conversion control means302A for limiting the regenerative amount from AC motor M1 so that powergeneration amount Pg1 is equal to or less than energy consumption Pm2.

In response to signal DTE6 from determination unit 56B, control unit 60Agenerates no control signal. Therefore, the present state in AC motorsM1, M2 is held.

FIG. 12 is a flowchart illustrating an operation of processing a failurein up-converter 12 in the third embodiment. The flowchart shown in FIG.12 is the same as the flowchart shown in FIG. 8 except that stepsS16-19, S21 and S22 are added to the flowchart shown in FIG. 8. In theflowchart shown in FIG. 12, step S16 is inserted between steps S13 andS14, and steps S14, S15 are executed when a determination “No” is madeat step S16.

Referring to FIG. 12, upon the start of a series of operations, stepsS10-S13 are executed as described above. After step S13, determinationunit 56B determines whether energy Pm received from calculating unit 58Ais positive or negative (step S16). When it is determined that energy Pmis positive, determination unit 56B determines that AC motor M1 is inthe powering mode. Then, steps S14, S15 as described above are executedso that power generation amount Pg2 in AC motor M2 is controlled to beequal to or less than energy consumption Pm1 in AC motor M1.

More specifically, determination unit 56B generates and outputs signalDTE3 to control unit 60A. In response to signal DTE3 from determinationunit 56B, control unit 60A regards energy Pm from calculating unit 58Aas energy consumption Pm1 in AC motor M1. Calculating unit 58Acalculates power generation amount Pg2 in AC motor M2 based on voltageVm from voltage sensor 13 and motor current MCRT2 from current sensor 28(step S14) and outputs the calculated power generation amount Pg2 tocontrol unit 60A. Control unit 60A compares power generation amount Pg2from calculating unit 58A with energy consumption Pm1, generates signalRDN to be output to engine ECU 65 for setting the rotation number ofengine 55 such that power generation amount Pg2 is equal to or less thanenergy consumption Pm1, and generates signal RGE2 to be output tovoltage conversion control means 302A. In response to signal RDN fromcontrol unit 60A, engine ECU 65 sets the rotation number of engine 55such that power generation amount Pg2 is equal to or less than energyconsumption Pm1. AC motor M2 therefore generates electric power equal toor less than energy consumption Pm1. In response to signal RGE2 fromcontrol unit 60A, voltage conversion control means 302A generates andoutputs signal PWMI23 to inverter 31. NPN transistors Q3-Q8 of inverter31 are turned on/off in response to signal PWMI23 and convert the ACvoltage generated by AC motor M2 to a DC voltage (step S15).

On the other hand, when it is determined that energy Pm is negative atstep S16, determination unit 56B determines that AC motor M1 is in theregenerative mode and generates signal DTE4 to be output to control unit60A. Then, in response to signal DTE4 from determination unit 56B,control unit 60A generates signal CUT to be output to engine ECU 65 andgenerates torque command value TRE to be output to phase voltagecalculating unit 40A and calculating unit 58A.

Engine ECU 65 is responsive to signal CUT to cut off the fuel for engine55 (step S17). Phase voltage calculating unit 40A calculates a voltageto be applied to each phase of AC motor M2 based on torque command valueTRE from control unit 60A, output voltage Vm from voltage sensor 13 andmotor current MCRT2 from current sensor 28 and outputs the calculatedvoltage to PWM signal converting unit 42. PWM signal converting unit 42generates signal PWMI21 for actually turning on/off each of NPNtransistors Q3-Q8 of inverter 31, based on the calculated voltage fromphase voltage calculating unit 40A, and outputs the generated signalPWMI21 to each of NPN transistors Q3-Q8 of inverter 31. NPN transistorsQ3-Q8 of inverter 31 are turned on/off in response to signal PWMI2 1,and inverter 31 drives AC motor M2 to output positive torque. AC motorM2 thereby outputs positive torque and rotates engine 55 at least at aprescribed rotation number (step S18).

Calculating unit 58A receives torque command value TRE from control unit60A to calculate energy consumption Pm2 in AC motor M2 based on torquecommand value TRE and motor rotation number MRN2 from external ECU (stepS19). In addition, calculating unit 58A calculates the sum of energy Pmcalculated at step S13 and energy consumption Pm2 as the sum Pg1+Pm2 ofpower generation amount Pg1 in AC motor M1 and energy consumption Pm2,and outputs the calculated sum to determination unit 56B.

Then, determination unit 56B determines whether the sum Pg1+Pm2 ispositive or negative (step S21). When it is determined that the sumPg1+Pm2 is negative, determination unit 56B generates and outputs signalDTE5 to control unit 60A. In response to signal DTE5 from determinationunit 56B, control unit 60A regards energy Pm from calculating unit 58Aas power generation amount Pg1 in AC motor M1 and compares powergeneration amount Pg1 with energy consumption Pm2 from calculating unit58A. Control unit 60A then generates and outputs signal RGE1 to voltageconversion control means 302A for limiting the regenerative amount fromAC motor M1 so that power generation amount Pg1 is equal to or less thanenergy consumption Pm2.

In response to signal RGE1 from control unit 60A, voltage conversioncontrol means 302A generates and outputs signal PWMI13 to inverter 14for limiting power generation amount Pg1 to energy consumption Pm2 orless. NPN transistors Q3-Q8 of inverter 14 are turned on/off in responseto signal PWMI13, and power generation amount Pg1 in AC motor M1 islimited to energy consumption Pm2 in AC motor M2 or less (step S22).

On the other hand, when it is determined that the sum Pg1+Pm2 ispositive at step S21, determination unit 56B outputs signal DTE6 tocontrol unit 60A. Control unit 60A then receives signal DTE6 fromdetermination unit 56B to generate no control signal. AC motor M1thereby produces power generation amount Pg1 equal to energy Pmcalculated at step S13, and AC motor M2 consumes energy consumption Pm2calculated at step S19. In other words, AC motors M1, M2 are held at thepresent state. A series of operations then ends.

At step S18 shown in FIG. 12, AC motor M2 is controlled such that itoutputs positive torque, when AC motor M1 is in the regenerative mode.In this way, the third embodiment is characterized in that when AC motorM1 not connected to engine 55 is in the regenerative mode, AC motor M2connected to engine 55 is controlled such that it outputs positivetorque. In other words, the energy consumption in AC motor M2 isincreased in order to prevent a voltage equal to or higher than thewithstand voltage from being applied to capacitor C2.

Returning to FIG. 9, the entire operation in voltage converting device100B will be described. Upon the start of the entire operation, controldevice 30B generates and outputs signal SE of H level to system relaysSR1, SR2 to turn on system relays SR1, SR2. DC power supply B outputs aDC voltage to up-converter 12 via system relays SR1, SR2.

Voltage sensor 10 detects DC voltage Vb output from DC power supply Band outputs the detected DC voltage Vb to control device 30B. Voltagesensor 13 detects voltage Vm on both ends of capacitor C2 and outputsthe detected voltage Vm to control device 30B. Current sensor 24 detectsmotor current MCRT1 flowing to AC motor M1 and outputs the detectedcurrent to control device 30B. Current sensor 28 detects motor currentMCRT2 flowing to AC motor M2 and outputs the detected current to controldevice 30B. Control device 30B receives torque command values TR1, TR2and motor rotation numbers MRN1, MNR2 from external ECU.

Control device 30B then generates signal PWMI11, based on DC voltage Vb,output voltage Vm, motor current MCRT1, torque command value TR1, andmotor rotation number MRN1, following the aforementioned method, andoutputs the generated signal PWMI11 to inverter 14. Control device 30Balso generates signal PWMI21 based on DC voltage Vb, output voltage Vm,motor current MCRT2, torque command value TR2, and motor rotation numberMRN2, following the aforementioned method, and outputs the generatedsignal PWMI21 to inverter 31.

In addition, when inverter 14 (or 31) drives AC motor M1 (or M2),control device 30B generates signal PWMU for controlling the switchingof NPN transistors Q1, Q2 of up-converter 12, based on DC voltage Vb,output voltage Vm, motor current MCRT1 (or MCRT2), torque command valueTR1 (or TR2), and motor rotation number MRN1 (or MRN2), and outputs thegenerated signal PWMU to up-converter 12.

Then, in response to signal PWMU, up-converter 12 up-converts DC voltageVb from DC power supply B and supplies the up-converted DC voltage tocapacitor C2 via nodes N1, N2. Inverter 14 then converts the DC voltagesmoothed by capacitor C2 to an AC voltage, according to signal PWMI11from control device 30B, for driving AC motor M1. Inverter 31 convertsthe DC voltage smoothed by capacitor C2 to an AC voltage, according tosignal PWMI21 from control device 30B, for driving AC motor M2.Therefore, AC motor M1 generates torque as designated by torque commandvalue TR1, and AC motor M2 generates torque as designated by torquecommand value TR2.

When the hybrid or electric vehicle including voltage converting device100B is in the regenerative braking mode, control device 30B receivessignal RGE from external ECU, and in response to the received signalRGE, generates signals PWM13, 23 to be output to inverters 14, 31,respectively, and generates signal PWMD to be output to up-converter 12.

Inverter 14 then converts the AC voltage generated by AC motor M1 to aDC voltage in response to signal PWM13 and supplies the converted DCvoltage to up-converter 12 via capacitor C2. Inverter 31 converts the ACvoltage generated by AC motor M2 to a DC voltage in response to signalPWM23 and supplies the converted DC voltage to up-converter 12 viacapacitor C2. Then, up-converter 12 receives the DC voltage fromcapacitor C2 via nodes N1, N2, down-converts the received DC voltageaccording to signal PWMD, and supplies the down-converted DC voltage toDC power supply B. The electric power generated by AC motor M1 or M2 isthereby charged in DC power supply B.

Control device 30B detects a failure in up-converter 12 following theaforementioned method and determines whether AC motor M1 is in thepowering mode or in the regenerative mode based on energy Pm in AC motorM1. If AC motor M1 is in the powering mode, control device 30B controlsAC motor M2 such that power generation amount Pg2 in AC motor M2 isequal to or less than energy consumption Pm1 in AC motor M1. If AC motorM1 is in the regenerative mode, control device 30B controls AC motor M1such that power generation amount Pg1 in AC motor M1 is equal to or lessthan energy consumption Pm2 in AC motor M2.

Therefore, a voltage equal to or higher than a withstand voltage isprevented from being applied to capacitor C2 even if up-converter 12fails.

It is noted that the failure processing method in accordance with thepresent invention includes, according to the flowchart shown in FIG. 12,detecting a failure in up-converter 12 and controlling power generationamount Pg1 in AC motor M1 to be equal to or less than energy consumptionPm2 in AC motor M2 or controlling power generation amount Pg2 in ACmotor M2 to be equal to or less than energy consumption Pm1 in AC motorM1.

The failure processing in motor torque control means 301B is actuallycontrolled by CPU. CPU reads a program including the steps of theflowchart shown in FIG. 12 from ROM and executes the read program tocontrol the failure processing for up-converter 12 according to theflowchart shown in FIG. 12. Therefore, ROM corresponds to a computer(CPU) readable recording medium with a program recorded thereon with thesteps of the flowchart shown in FIG. 12.

AC motors M1, M2 form “electric loads (including first and secondelectric loads)”.

Other details are the same as in the first embodiment.

In accordance with the third embodiment, the voltage converting deviceincludes a control device that controls a power generation amount in oneof two AC motors to be equal to or less than energy consumption in theother AC motor in the event of a failure in an up-converter, therebypreventing application of a voltage equal to or higher than a withstandvoltage to a capacitor provided at an input of an inverter.

It is noted that the present invention is not limited to the disclosurein the embodiments above and is applicable to a variety of hybrid orelectric vehicles. For example, a plurality of inverters and motors maybe connected in parallel to capacitor C2 and each motor (or motorgenerator) may be driven independently. In this case, one motor may beused for driving a rear wheel and the other motor may be used fordriving a front wheel. A hybrid vehicle using a planetary gear mechanismis known where one motor generator is connected to a sun gear of theplanetary gear mechanism, an engine is connected to a carrier of theplanetary gear mechanism, and the other motor generator is connected toa ring gear. The present invention is also applicable to such a hybridvehicle.

Although the present invention has been described and illustrated indetail, it is clearly understood that the same is by way of illustrationand example only and is not to be taken by way of limitation, the spiritand scope of the present invention being limited only by the terms ofthe appended claims.

INDUSTRIAL APPLICABILITY

The present invention is applied to a voltage converting device capableof processing a failure in an up-converter without improving withstandvoltage performance of a capacitor placed at an input of an inverter.The present invention is also applied to a failure processing methodcapable of processing a failure in an up-converter without improvingwithstand voltage performance of a capacitor placed at an input of aninverter. The present invention is further applied to a computerreadable recording medium with a program recorded thereon for causing acomputer to execute failure processing for an up-converter withoutimproving withstand voltage performance of a capacitor placed at aninput of an inverter.

1. A voltage converting device comprising: an electric load having an electric power generating function; a capacitor connected to an input of said electric load; a down-converter down-converting a voltage of said capacitor; first control means controlling an amount of electric power generated by said electric load; and second control means outputting to said first control means a command for instructing prohibition of electric power generation in said electric load or for instructing decrease in an amount of electric power generated by said electric load, when said down-converter fails.
 2. The voltage converting device according to claim 1, wherein said down-converter has a voltage-up-converting function.
 3. The voltage converting device according to claim 1 wherein said electric load is a motor having an electric power generating function, said second control means outputs to said first control means a command for instructing restriction of a regenerative electric power generating function of said motor when said down-converter fails, and said first control means restricts an amount of regenerative electric power generated by said motor based on said command.
 4. The voltage converting device according to claim 3, wherein said second control means outputs to said first control means a command for instructing prohibition of regenerative electric power generation of said motor, and said first control means controls said amount of regenerative electric power generated by said motor to zero based on said command.
 5. The voltage converting device according to claim 3, further comprising another electric load different from said motor, wherein said second control means outputs to said first control means a command for instructing restriction of said amount of regenerative electric power generated by said motor to a value smaller than power consumption in said another electric load, and said first control means restricts said amount of regenerative electric power generated by said motor based on said command.
 6. A voltage converting device comprising: a first electric load having an electric power generating function; a capacitor connected to an input of said first electric load; a down-converter down-converting a voltage of said capacitors; a second electric load that operates by receiving electric power generated by said first electric load; first control means controlling an amount of power consumption in said second electric load; and second control means outputting to said first control means a command for instructing increase in an amount of power consumption in said second electric load, when said down-converter fails.
 7. The voltage converting device according to claim 6, wherein said second electric load is a motor, said first control means further controls torque of said motor, said second control means outputs to said first control means a command for instructing said motor to output positive torque, and said first control means controls the torque of said motor to a positive value based on said command.
 8. A computer readable recording medium with a program recorded thereon for causing a computer to execute failure processing in a voltage converting device, said voltage converting device including an electric load having an electric power generating function, a capacitor connected to an input of said electric load, and a down-converter down-converting a voltage of said capacitor, wherein said program causes the computer to execute a first step of generating a command for instructing prohibition of electric power generation in said electric load or for instructing decrease in an amount of electric power generated by said electric load, when said down-converter fails, and a second step of controlling an amount of electric power generated by said electric load based on the command generated in said first step.
 9. The computer readable recording medium with a program recorded thereon according to claim 8, wherein said electric load is a motor having an electric power generating function, and in said first step, a command for instructing restriction of a regenerative electric power generating function of said motor is generated.
 10. The computer readable recording medium with a program recorded thereon according to claim 9, wherein in said first step, a command for instructing prohibition of regenerative electric power generation of said motor is generated.
 11. The computer readable recording medium with a program recorded thereon according to claim 9, wherein said voltage converting device further includes another electric load different from said electric load, and in said first step of said program, a command for instructing restriction of an amount of regenerative electric power generated by said motor to a value smaller than power consumption in said another electric load is generated.
 12. A computer readable recording medium with a program recorded thereon for causing a computer to execute failure processing in a voltage converting device, said voltage converting device including a first electric load having an electric power generating function, a capacitor connected to an input of said electric load, a down-converter down-converting a voltage of said capacitor, and a second electric load that operates by receiving electric power generated by said first electric load, wherein said program causes the computer to execute a first step of generating a command for instructing increase in an amount of power consumption in said second electric load, when said down-converter fails, and a second step of controlling an amount of power consumption in said second electric load, based on the command generated in said first step.
 13. The computer readable recording medium with a program recorded thereon according to claim 12, wherein said second electric load is a motor, and in said first step of said program, a command for instructing said motor to output positive torque is generated when said down-converter fails, and in said second step, the torque of said motor is controlled to a positive value based on the command generated in said first step.
 14. A failure processing method in a voltage converting device, said voltage converting device including an electric load having an electric power generating function, a capacitor connected to an input of said electric load, and a down-converter down-converting a voltage of said capacitor, said failure processing method comprising: a first step of generating a command for instructing prohibition of electric power generation in said electric load or for instructing decrease in an amount of electric power generated by said electric load, when said down-converter fails; and a second step of controlling an amount of electric power generated by said electric load based on the command generated in said first step.
 15. The failure processing method according to claim 14, wherein said electric load is a motor having an electric power generating function, and in said first step, a command for instructing restriction of a regenerative electric power generating function of said motor is generated.
 16. The failure processing method according to claim 15, wherein in said first step, a command for instructing prohibition of regenerative electric power generation of said motor is generated.
 17. The failure processing method according to claim 15, wherein said voltage converting device further includes another electric load different from said electric load, and in said first step of said failure processing method, a command for instructing restriction of an amount of regenerative electric power generated by said motor to a value smaller than power consumption in said another electric load is generated.
 18. A failure processing method in a voltage converting device, said voltage converting device including a first electric load having an electric power generating function, a capacitor connected to an input of said electric load, a down-converter down-converting a voltage of said capacitor, and a second electric load that operates by receiving electric power generated by said first electric load, wherein said failure processing method comprising: a first step of generating a command for instructing increase in an amount of power consumption in said second electric load, when said down-converter fails; and a second step of controlling an amount of power consumption in said second electric load, based on the command generated in said first step.
 19. The failure processing method according to claim 18, wherein said second electric load is a motor, and in said first step of said failure processing method, a command for instructing said motor to output positive torque is generated when said down-converter fails, and in said second step, the torque of said motor is controlled to a positive value based on the command generated in said first step.
 20. The voltage converting device according to claim 2 wherein said electric load is a motor having an electric power generating function, said second control means outputs to said first control means a command for instructing restriction of a regenerative electric power generating function of said motor when said down-converter fails, and said first control means restricts an amount of regenerative electric power generated by said motor based on said command. 